Method of producing cellulated articles



2,860,997 METHODJOF PRODUCINGICELLULATED,

, ARTICLES 4 Dominic DEustachio, Port Allegany, Pa., assignor to Pittsburgh"CornihgaCorporatioir, littsburgh, 'Pa., a corporation' of Pennsylvania No Drawing. Original application March "21, "19 5 2,,Se-

rial No; 277,895; now' Pate'nt No. 2,775,524,. dated December 255 1956; Divided' am nes-application August 14, 1956, Serial No. 603,87 9

1.Claim. c roe-40 Patent 2,775,524.

'It has heretofore been proposedto prepare :a material suitable for use as a heat insulator and for floats in life rafts and isimilarrpurposesrby finely crushing glass cullet containing sulfatesand/oncertain metal-oxides such as antimony oxide, admixing the ground glass with acarbon black, powdered coal,- or "othercarbonaceous material and then heating-the-mixture"to'a temperature sufiicienfto sinter -andtcellulate-theglass; The sin tering temperature is' -t'hetemperature-atwhich theglass' particles become soft and adhere :togetherxbyqcontact:.,j j

As a result of. the heating operation, a chemicaLreaction takes place, at the temperature. approximatingor slightly above the temperature of'th'e sintering'of the glass, between the carbon and the sulfates and/or metal oxides in the glass. Gases such as sulfur dioxide, carbon dioxide, and other gases are generated in situ in the sintered mass and are entrapped as bubbles which impart to the mass a cellular structure and result in a product of light weight and high resistance to the transmission of heat by conduction and radiation. The cell structures are in most cases sealed so that water, liquid, or vapor and chemical fumes cannot permeate the mass.

The material as heretofore obtained was black in color due to the presence of free carbon in the sintered mass. The presence of these entrapped particles of carbon is believed to reduce the thickness of the cell walls and thus facilitates to a small degree the penetration of moisture through the cellulated glass at high temperatures.

It was thought that the presence of the carbon in the cellulated glass could be eliminated by merely reducing the amount of the carbon used in the cellulating batch so that all the carbon would be oxidized to a gas and none would remain as carbon. reduction of the amount of carbon below a critical point seriously reduced the amount of cellulation and that carbon still remained in the cellulated product when employed in amounts slightly below this critical point. This minimum amount of carbon varies with the type of glass to be cellulated and with the gassing agents employed. In the case of cellulating a ground lime-soda glass containing antimony oxide, the minimum amount of carbon which can be employed to give good cellulation is about 0.2 percent by weight of the ground batch.

The explanation of the requirement of such a minimum amount of carbon to achieve good cellulation appears to be that one clump of carbon particles is needed for each cell formed to act as a nucleus for starting the formation However, it was found that the 2,860,997 Patented Nov. 18, 1958 "ice of the cell. Thus it can be seen that it is necessary to provide as uniform and as high a degree of mixing of the carbon and ground glass as possible to achieve good uniform cellulation.

The best means known at the present for achieving such intimate mixture is to grind the glass and carbon together in a ball mill. ing mixture are larger than they need .be.but.furthe r; subdivision isextreniely difficult because the large. number of relatively fine glass Particles cushions the-blows-of the balls and cuts.grinding efliciencyaand mixin g toavery low figure after a certain meshsizeis reached v .In accordance :with the presentinvention, amoreeflicient method of utilizing carbon .in the above described process for m'akingcellular glass hasbeen discovered. This method comprises employing carbon or carbonaceous material prepared as a coating on an inert substance having a high surface areafor agiven weight, for example, having a surface area-abovelOsquare meters per gram of inert substance and preferably above-50 square meters per gram-of inertsubstance. .Such high surface area substances are inert With-respect to the. glass, and gassing agents and include diatomaceous-earthand sp,eci-. allyprepared substanceshavinga high surface area such as specially prepared silicas and-calcium silicates;

Thecarbon may be prepared by absorbing on' the di'-' atomaceous earth or silica a solution of sugarror-other carbon-containing substance, which substance'will readily decompose to carbon upon heating;or treating withl-a. re: ducingagent; Other carbon-containing compounds-Which may housedinclude glycerol or otheppolyhydric-alcor hols;v The carbon also may. be;;prepared. by mixing na slurry of finely divided carbon .with.-.the-,high,surface :area inert substance, such as diatomaceous earth rto insert the carbon particles windhe skeleton-like structure of the dia tomaceousearth andthendrying thernixturezl The weight r n loe lia tt l a e y; ary from 1 t 50 parts carbon in parts inert substance.

A sufiicient quantity, for example, from 0.2 to 0.8 percent by weight, of this prepared diatomaceous earth or silica is added to the ground glass, mixed and pulverized in a ball mill and then heated to a temperature sufficient to sinter and cellulate the glass as described above to produce the cellulated glass.- Temperatures of from 1400 to 1800 F. are suitable in most instances. A high degree of cellulation is obtained by this process and less than one-half the amount of carbon previously required is used. Cellulated products thus produced are more resistant to moisture penetration than cellulated products produced according to presently known methods.

The silica skeleton of the diatomaceous earth keeps the carbon particles separated from each other. use of such carbon-containing silica provides a greater volume of material for grinding with less carbon and enables a more eflicient distribution of the carbon to be attained. The presence of the diatomaceous earth or silica in the product is not harmful.

The following examples are illustrative of the invention:

Example I Silica containing carbon was prepared in the following manner. Ten grams of a silica having a surface area of approximately 100 square meters per gram were mixed with 20 grams of sugar and 10 grains of water, stirred to a uniform paste, evaporated to dryness, and then heated with a limited supply of air to 300 C. for two hours to form a black char.

The resulting black char was mixed with glass cullet in four different batches using 0.2, 0.4, 0.8, and 1.6 grams of char to 100 grams of glass. The glass was typical The carbon clumps present in such result- 7 The i lime-soda glass containing about 1.0 percent of antimony oxide.

These mixtures were each ground for about five hours in a ball mill maintained at a temperature of 80 F. Thereafter, the mixtures were placed in a crucible which was then covered and the mixture was heated to a temperature of about 1600 F. for thirty minutes and cellulated glass was obtained. The sample in which only 0.2 gram of char per 100 grams of glass was employed was nearly white. 1

Example 11 Mixtures of equal parts of sugar and a silica having a surface area of approximately 100 square meters per gram were prepared in an aqueous solution and a char was produced as in Example I. Various amounts of this char were mixed with ground glass and cellulated as in Example-I. In all cases, good cellulation was obtained when 0.08 to 0.15 percent by weight of carbon was present. With the lower values of carbon, a light colored cellulated glass was obtained.

Example III Mixtures of a silica having a surface area of approximately 100 square meters per gram and a commercial aqueous suspension of carbon black in which the carbon has a particle size of about 12 millimicrons were prepared containing 6, 12, 25, and 50 percent carbon by weight of the mixture of carbon and silica. The mixtures were heated at 120 C. for one hour to evaporate the water. Portions of these mixtures were added to ground glass as in Example I, ground for five hours in a ball mill, and then heated to a temperature of 1630" F. to cellulate the mixture. Two tests were run for each percentage of carbon as prepared above. The amounts of the mixture added to the glass for each percentage were 0.6 and 0.8 percent by weight of the mixture of the glass and prepared carbon.

The invention is applicable wherever carbon is to be used as the gassing agent in the cellulation of vitreous material such as glass or other materials which may be cellulated such as slag, silica, glass batch materials, na-

. lead, iron, titanium, aluminum, molybdenum, vanadium,

tungsten, etc.

Although the present invention has been described with particular reference to the specific details of certain embodiments thereof, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claim.

I claim:

A method of preparing cellular glass, which comprises mixing a slurry of finely divided carbon with an inert material selected from the group consisting of diatomaceous earth and silica and having a surface area greater than about 10 square meters per gram, drying the mixture, said mixture containing carbon in an amount from 5 to parts by weight to parts of said inert material, grinding glass cullet with an amount of said mixture to provide from 0.08 to 0.15 percent by weight of carbon based on the weight of said cullet, heating the ground mixture to a temperatupre sufiicient to soften and cellulate the glass, and cooling the product.

References Cited in the file of this patent UNITED STATES PATENTS 1,448,846 Jordan Mar. 20, 1923 1,589,532 Hoodless June 22, 1926 2,596,669 Ford May 13, 1952 2,775,524 D'Eustachio Dec. 25, 1956 OTHER REFERENCES Jacobson: Silica Black, Ind. and Eng. Chem., July 1934 (pages 798-800). 

